1. Field of the Invention
The present invention relates in general to a light source controlling circuit for controlling a light source for emitting continuous light and a portable electronic apparatus having a camera function, and more particularly to a circuit for detecting an abnormal state of the light source to stop the emission of light from the light source.
2. Description of the Related Art
In recent years, many portable electronic apparatuses such as a mobile telephone have an imaging element and can operate as cameras. Some portable electronic apparatuses each having an imaging element have light sources with each of which the photography can be made under an environment having low illuminance. In general, however, a temperature of a light source built in a camera reaches a high temperature during the operation, and hence harms an electronic apparatus within the camera in some cases. JP 2001-66675 A, JP 2001-242510 A, and JP 2002-156690 A disclose techniques for suppressing heat generation of a flash light emitting device such as a xenon lamp built in a camera. However, JP 2001-66675 A, JP 2001-242510 A, and JP 2002-156690 A do not treat a continuous light emitting device as an object. Consequently, any of those disclosed techniques cannot be applied to a problem with respect to the heat generation of the light source for emitting continuous light which the present invention aims at solving.
Referring to FIG. 1, there is shown an example of a control circuit for a light emitting diode (LED) mounted within a portable electronic apparatus having an imaging element. The LED 103 is a light source for the portable electronic apparatus and serves to emit continuous light. A light source controlling circuit shown in FIG. 1 includes the LED 103, an LED power supply circuit 102, a CPU 101, and a power supply 104. The LED 103 emits a sufficient quantity of continuous light to a subject under an environment having low illuminance. For example, the LED 103 may be configured in the form of an LED array having a plurality of LEDs connected in series with each other. The LED power supply circuit 102 adjusts a voltage supplied from the power supply 104 into a predetermined voltage, which is in turn supplied to the LED 103. The power supply 104 operates as a power supply not only for the LED 103 but also for the portable electronic apparatus, and for example, is any one of various kinds of batteries. The CPU 101 controls the overall portable electronic apparatus, and controls an operation of the LED power supply circuit 102. However, in the above light source controlling circuit, even when the voltage supplied to the LED 103 is held at a predetermined value, a temperature of the LED 103 reaches a temperature equal to or larger than the predetermined value due to a short circuit or the like in some cases. Since the above conventional light source controlling circuit does not include means for monitoring a lighting state or a heat radiation quantity (or a temperature) of the LED 103, the malfunction of the light source as described above is not detected.